Silica-based sols

ABSTRACT

The invention relates to a sol containing silica-based particles having an axial ratio of at least about 10 and specific surface area of at least about 600 m2/g. The invention further relates to a sol containing silica-based particles having an axial ratio of at least about 10 and S-value up to about 25. The invention further relates to a sol containing silica-based particles having an axial ratio of at least about 10 and a specific surface area of at least about 400 m2/g, wherein the silica-based particles are surface-modified. The invention further relates to a sol containing silica-based particles having a viscosity of at least 50 cP and silica content of at least about 3% by weight, wherein the silica-based particles have a specific surface area of at least about 400 m2/g. The invention further relates to a process for producing the aqueous silica-based sol according to the invention, a sol containing silica-based particles obtainable by the process, use of the sol containing silica-based particles as a flocculating agent. The invention further relates to a process for producing paper in which the sol containing silica-based particles is used as a drainage and retention aid.

FIELD OF THE INVENTION

The present invention relates to silica-based sols and their productionand use. The present invention provides silica-based sols with highstability and SiO₂ contents as well as improved drainage and retentionperformance in papermaking.

BACKGROUND OF THE INVENTION

In the papermaking art, an aqueous suspension containing cellulosicfibers, and optional fillers and additives, is fed into a headbox whichejects the cellulosic suspension onto a forming wire. Water is drainedfrom the cellulosic suspension to provide a wet paper web which isfurther dewatered and dried in the drying section of the paper machine.Drainage and retention aids are conventionally introduced into thecellulosic suspension to facilitate drainage and increase adsorption offine particles onto the cellulosic fibers so that they are retained withthe fibers.

Sols of silica-based particles are widely used as drainage and retentionaids, usually in combination with charged organic polymers. Suchadditive systems are among the most efficient now in use in thepapermaking industry, in particular those comprising silica-based solswhich contain microgel or aggregated particles of high surface areas.Examples of silica-based sols of this type include those disclosed inU.S. Pat. Nos. 5,176,891; 5,368,833; 5,603,805 and 6,372,806 as well asInternational Patent Appl'n Pub. Nos. WO 98/30753; 98/56715; 00/66491;00/66492; 2005/097678 and 2005/100241.

Spherical silica-based particles can grow and aggregate in various waysdepending on the conditions. Under certain conditions, the particlesgrow symmetrically, thus maintaining a spherical shape. Under otherconditions, the spherical particles aggregate to clusters of particlesand form three dimensional networks and microgels. Silica-basedparticles may also form elongated aggregates that are more or lesslinear, thus forming aggregates with different degrees of aggregation indifferent directions or axes.

High surface area aqueous silica-based sols containing microgel usuallyhave poor stability and high dilution is normally necessary to avoidcomplete gelation. Because of the stability problems associated withsuch products, and the prohibitive cost of shipping stable but extremelydilute products, high surface area aqueous silica-based sols containingmicrogel are preferably prepared at the location of intended use, forexample at the paper mill.

Sols of aggregated silica-based particles can be defined by means ofdifferent parameters, including S-value and axial ratio. The S-valueindicates the degree of aggregate or microgel formation; a lower S-valueis indicative of a higher degree of aggregation of the silica-basedparticles. The axial ratio is applicable to elongated aggregates ofsilica particles and indicates the ratio of the long axis to the shortaxis.

It would be advantageous to be able to provide silica-based sols withimproved drainage and retention performance. It would also beadvantageous to be able to provide silica-based sols and, in particular,aggregate or microgel containing silica-based sols with improved surfacearea stability at very high surface areas and SiO₂ contents. It wouldalso be advantageous to be able to provide a method for producing suchsilica-based sols. It would also be advantageous to be able to provide apapermaking process with improved drainage and retention performance.

SUMMARY OF THE INVENTION

The present invention is generally directed to a sol containingsilica-based particles having an axial ratio of at least 10 and aspecific surface area of at least 600 m²/g.

The present invention is further generally directed to a sol containingsilica-based particles having an axial ratio of at least about 10 and anS-value up to about 35.

The present invention is further generally directed to a sol containingsilica-based particles having an axial ratio of at least 10 and aspecific surface area of at least about 400 m²/g, wherein thesilica-based particles are surface-modified.

The present invention is further generally directed to a sol containingsilica-based particles having a viscosity of at least 50 cP and silicacontent of at least about 3% by weight, wherein the silica-basedparticles have a specific surface area of at least about 400 m²/g.

The present invention is further generally directed to a process forproducing a sol containing silica-based particles which comprises:

-   -   (a) providing a reaction vessel containing water and a cationic        ion exchange resin having at least part of its ion exchange        capacity in hydrogen form;    -   (b) adding to said reaction vessel an aqueous alkali metal        silicate at a rate of at least about 400 g SiO₂ per hour and kg        ion exchange resin present in the reaction vessel to form an        aqueous silicate slurry;    -   (c) stirring said aqueous silicate slurry until the pH of the        aqueous phase is in the range of from about 5.0 to about 9.0;    -   (d) adding one or more alkaline materials to the aqueous phase        to form a pH in the range of from about 7.0 to about 11.0; and    -   (e) separating said ion exchange resin from the aqueous phase        after step (c) or after step (d).

The present invention is also generally directed to a process forproducing a sol containing silica-based particles which comprises:

-   -   (a) providing a reaction vessel containing water and a cationic        ion exchange resin having at least part of its ion exchange        capacity in hydrogen form;    -   (b) adding to said reaction vessel an aqueous alkali metal        silicate to form an aqueous silicate slurry;    -   (c) stirring said aqueous silicate slurry until the pH of the        aqueous phase is in the range of from about 5.0 to about 8.5;    -   (d) adding one or more alkaline materials to the aqueous phase        to form a pH in the range of from about 7.0 to about 8.5; and    -   (e) separating said ion exchange resin from the aqueous phase        after step (c) or after step (d).

The invention is further directed to a sol containing silica-basedparticles obtainable by the process according to the invention.

The invention is further directed to various uses of the sol containingsilica-based particles according to the invention such as a flocculatingagent, in particular as a drainage and retention aid in papermaking andas a flocculating agent for water purification.

The invention is further generally directed to a process for producingpaper which comprises

-   -   (a) providing an aqueous suspension comprising cellulosic        fibers;    -   (b) adding to the suspension one or more drainage and retention        aids comprising a sol containing silica-based particles        according to the invention; and    -   (c) dewatering the obtained suspension to provide a sheet or web        of paper.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention there is provided solscontaining silica-based particles, also referred to herein assilica-based sols, which are suitable for use as flocculating agents inpapermaking and water purification, in particular as drainage andretention aids in papermaking. The term “drainage and retention aids”,as used herein, refers to one or more additives which, when added to anaqueous cellulosic suspension, give better drainage and/or retentionthan what is obtained when not adding the said one or more additives.The silica-based sols of the invention exhibit good stability overextended periods of time, notably high axial ratio and surface areastability and high stability to complete gel formation. The silica-basedsols further result in improved drainage and retention when used inpapermaking. Hereby the present invention makes it possible to increasethe speed of the paper machine and to use a lower dosage of additive togive a corresponding drainage and retention effect, thereby leading toan improved paper making process and economic benefits.

The aqueous silica-based sol according to the invention containssilica-based particles, i.e. particles based on silica or SiO₂, that arepreferably anionic and preferably colloidal, i.e., in the colloidalrange of particle size. Aqueous dispersions of this type are usuallyreferred to as sols. Preferably, the silica-based particles have beenprepared by condensation polymerisation of siliceous compounds, e.g.silicic acids and silicates, which can be homo or co-polymerised. Thesilica-based sols can be modified and contain other elements, e.g.aluminum, boron, nitrogen, zirconium, gallium and titanium, which can bepresent in the aqueous phase of the sol and/or in the silica-basedparticles. Such elements may also be present in the silica-based sols asimpurities.

The silica based sols according to the invention contains asymmetric orelongated silica-based particles. Preferably, such asymmetric particlesare modelled as ellipsoids of revolution characterised by the axialratio, i.e. the ratio of the long axis to the short axis. Particleasymmetry affects the translational and rotational diffusioncoefficients of colloidal silica-based particles and also the viscosityof their sols or solutions. These properties can be used to determinethe axial ratio, either directly or indirectly, using a combination ofviscosity and dynamic light scattering. The silica-based sol of theinvention usually has an axial ratio of at least about 10 or at leastabout 11, suitably at least 12 and preferably at least 13. Usually, theaxial ratio is up to about 100 or up to about 50, suitably up to about40 and preferably up to about 35. The axial ratios given hereinrepresent the average axial ratio of the silica-based particles presentin a sol. The axial ratio is measured and calculated as described by D.Biddle, C. Walldal and S. Wall in Colloids and Surfaces, A:Physiochemical and Engineering Aspects 118 (1996), 89-95, determiningdimensions and axial ratios of equivalent unsolvated prolate ellipsoids.This ellipsoid model is characterised by the ratio between the longerdiameter (a) and the shorter diameter (b). The axial ratio is defined asa/b. The model used is a combination of data obtained from intrinsicviscosity measurements and dynamic light scattering measurements and therelations of Simha and Perrin for the intrinsic viscosity and fractionalfactors respectively of ellipsoids of revolution. These data can then beused to iterate a mathematical fit to the ellipsoid form, thus givingthe axial ratio describing the shape of the silica-based particles.

The silica-based sol of the invention usually has an S-value of at leastabout 4% or at least about 6%, suitably at least 8% and preferably atleast 10%. Usually, the S-value is up to about 50% or up to about 35%,suitably up to about 30% and preferably up to about 25%. The S-value ismeasured and calculated as described by R. K. Iler & R. L Dalton in J.Phys. Chem. 60 (1956), 955-957. The S-value of a silica-based solindicates the degree of aggregate or microgel formation and a lowerS-value is indicative of a higher degree of aggregate or microgelformation.

The silica-based particles present in the sol usually have a specificsurface area of at least about 400 m²/g or at least about 500 m²/g,suitably at least about 600 m²/g or at least about 700 m²/g, preferablyat least about 800 m²/g and more preferably at least about 1000 m²/g.The specific surface area is usually up to 1600 m²/g or at least about1500 m²/g , suitably up to about 1400 m²/g and preferably up to about1300 m²/g . The specific surface area is measured by means of titrationwith NaOH as described by G. W. Sears, Jr. in Analytical Chemistry 28(1956):12, 1981-1983, after appropriate removal of or adjustment for anycompounds present in the sample that may disturb the titration likealuminum and boron compounds, for example as described by Sears and inU.S. Pat. No. 5,176,891. The specific surface areas given hereinrepresent the average specific surface area of the silica-basedparticles present in a sol.

In one embodiment of the invention, the silica-based sol is modifiedwith aluminum. Examples of suitable aluminium compounds include thosedefined herein. According to this embodiment, the silica-based particlesare preferably at least surface-modified with aluminum. If modified withaluminum, the silica-based sol usually has a mole ratio of Si:Al of fromabout 1:1 to 40:1, suitably from about 3:1 to 30:1 and preferably fromabout 5:1 to 20:1.

In one embodiment of the invention, the silica-based sol is modifiedwith an organic nitrogen-containing compound. Examples of suitableorganic nitrogen-containing compounds include those defined herein.According to this embodiment, the silica-based particles are preferablyat least surface-modified with the organic nitrogen-containing compound.If modified with an organic nitrogen-containing compound, thesilica-based sol usually have a mole ratio of Si:N of from about 1:1 to50:1, suitably from about 2:1 to 40:1 and preferably from about 2.5:1 to25:1.

The silica-based sol of the invention usually has a mole ratio of Si:X,where X=alkali metal, of at least 5:1, suitably at least 6:1, preferablyat least about 7:1 and most preferably at least 8:1. The mole ratio ofSi:X, where X=alkali metal, is usually up to 30:1, suitably up to 20:1,preferably up to 15:1 and more preferably up to 12:1.

The silica-based sol of the invention usually has a pH of at least about6.0 or at least about 6.5, suitably at least about 7.0, at least about7.5 or at least about 8.0. Usually, the pH of the silica-based sol is upto about 12.0 or up to about 11.0, suitably up to about 10.5, up toabout 10.00, or even up to 9.5, up to about 9.0 or it can be up to 8.5or up to about 8.0.

The silica-based sol of the invention usually has a silica (SiO₂)content of at least about 2% by weight, suitably at least about 3 byweight or at least about 4 by weight and preferably at least about 5 byweight. Usually, the silica content is up to about 30% by weight or upto about 20 by weight, suitably up to about 15 by weight and preferablyup to about 10 by weight. In order to simplify shipping and reducetransportation costs, it is generally preferable to ship highconcentration silica-based sols according to the invention but it is ofcourse possible and usually preferable to dilute and mix thesilica-based sols to substantially lower silica contents prior to use,for example to silica contents within the range of from 0.05 to 2% byweight, in order to improve mixing with the furnish components.

The viscosity of the silica-based sol of the invention can varydepending on, for example, the silica content of the sol. Usually, theviscosity is at least about 5 cP, often at least about 10 cP or at leastabout 20 cP, and it may even be at least about 50 cP or at least 75 cP.Usually, the viscosity is up to about 200 cP or up to about 175 cP,suitably up to about 150 cP. The viscosity can be measured by means ofknown technique, for example using a Brookfield LVDV II+viscosimeter.

The silica-based sol of the invention is preferably stable. Preferably,the silica-based sol maintains certain of its parameters over a certainperiod of time. Usually, the sol maintains an axial ratio of at leastabout 10, suitably at least about 11 and preferably at least about 12for at least 3 months on storage or ageing at 20° C. in dark andnon-agitated conditions. Suitably, these axial ratios are maintained ata silica content of at least about 3 by weight and preferably at leastabout 5 by weight. Usually, the sol maintains a specific surface area ofat least about 400 m²/g or at least about 600 m²/g, suitably at leastabout 800 m²/g and more preferably at least about 1000 m²/g for at least3 months on storage or ageing at 20° C. in dark and non-agitatedconditions. Suitably, these specific surface areas are maintained at asilica content of at least about 3 by weight and preferably at leastabout 5 by weight. Usually, the sol maintains the above definedviscosity values for at least 3 months on storage or ageing at 20° C. indark and non-agitated conditions. Suitably, these viscosity values aremaintained at a silica content of at least about 3 by weight andpreferably at least about 5 by weight.

The silica-based sols of the invention can be produced by a process thatis simple, quick and easy to control and regulate.

Step (a) of the process comprises providing a reaction vessel comprisingan aqueous phase containing water and an ion exchange resin. The ionexchange resin used in the process is cationic and has at least part ofits ion exchange capacity in the hydrogen form, i.e. an acid cationicion exchange resin, preferably a weak acid cationic ion exchange resin.Suitably, the ion exchange resin has at least 40% of its ion exchangecapacity in the hydrogen form, preferably at least 50%. Suitable ionexchange resins are provided on the market by several manufacturers, forexample Amberlite™ IRC84SPI from Rohm & Haas. Preferably, a reactionvessel equipped with means for mixing, e.g. a stirrer, is charged withthe ion exchange resin and water. Preferably, the ion exchange resin isregenerated by addition of an acid, e.g. sulphuric acid, preferablyaccording to manufacturer's instruction.

Step (b) of the process comprises adding an aqueous alkali metalsilicate to the reaction vessel containing water and the ion exchangeresin, preferably regenerated ion exchange resin, to form an aqueoussilicate slurry. Usually, the aqueous alkali metal silicate is added tothe reaction vessel at a rate of at least about 400, suitably at leastabout 450 and preferably at least about 500 g SiO₂ per hour and kg ionexchange resin present in the reaction vessel. Usually, the rate is upto about 10000 or up to about 7000, suitably up to about 5000 andpreferably up to about 4000 g SiO₂ per hour and kg ion exchange resinpresent in the reaction vessel.

Examples of suitable aqueous alkali metal silicates or water glassinclude conventional materials, e.g. lithium, sodium and potassiumsilicates, preferably sodium silicate. The molar ratio of silica toalkali metal oxide, e.g. SiO₂ to Na₂O, K₂O or Li₂O, or a mixturethereof, in the silicate solution can be in the range of from 15:1 to1:1, suitably in the range of from 4.5:1 to 1.5:1, preferably from 3.9:1to 2.5:1. The aqueous alkali metal silicate used can have a SiO₂ contentof from about 2 to about 35% by weight, suitably from about 5 to about30% by weight, and preferably from about 15 to about 25% by weight. ThepH of the aqueous alkali metal silicate is usually above 11, typicallyabove 12.

According to a preferred embodiment of the invention, step (b) of theprocess comprises keeping or maintaining the temperature of the aqueoussilicate slurry that is formed at from at least about 0, suitably atleast about 5 and preferably at least about 10° C. up to about 80 or upto 50, suitably up to about 40 and preferably up to about 35° C. Thiscan be achieved by cooling or controlling the temperature of thereaction vessel while adding the aqueous alkali metal silicate to thereaction vessel containing water and the ion exchange resin.

Step (c) of the process comprises stirring the aqueous silicate slurryuntil its aqueous phase reaches a certain pH-value. Usually, the aqueousphase has a pH of at least about 5.0, suitably at least about 6.0 or atleast about 6.5, preferably at least about 7.0. Usually, the aqueousphase reaches a pH of up to about 9.0, suitably up to about 8.5 andpreferably up to about 8.0. Preferably, particle growth takes placewhile stirring the aqueous silicate slurry. The silica-based particlesformed usually have a specific surface area of at least 300 m²/g,suitably at least about 600 m²/g and preferably at least about 1000m²/g. The specific surface area is usually very high, for example up toabout 1600 m²/g or up to about 1400 m²/g. Suitably, the slurry isstirred to allow particle aggregation and, preferably, formation ofelongated aggregates of silica-based particles. The stirring usuallytakes place during a period of time of from about 1 to about 480minutes, suitably from about 3 to about 120 minutes and preferably fromabout 5 to about 60 minutes.

According to one embodiment of the invention, step (c) of the processcomprises keeping or maintaining the temperature of the aqueous silicateslurry while being stirred at from at least about 0° C., suitably atleast about 5° C. and preferably at least about 10° C. up to about 80°C. or up to 50° C., suitably up to about 40° C. and preferably up toabout 35° C. This can be achieved by cooling or controlling thetemperature of the reaction vessel while stirring the aqueous silicateslurry.

If desired, additional water can be to the reaction vessel during orafter step (c) to lower the viscosity of the aqueous phase and reducethe speed of particle growth, particle aggregation and formation ofelongated aggregates of silica-based particles.

Step (d) of the process comprises adding one or more alkaline materialsto the aqueous phase. Usually, the addition of said one or more alkalinematerials increases the pH of the aqueous phase to at least about 6.0 orat least about 6.5, suitably at least about 7.0, at least about 7.5 orat least about 8.0. Usually, the pH of the aqueous phase is up to about12.0 or up to about 11.0, suitably up to about 10.5, up to about 10.00,or even up to 9.5, up to about 9.0 or it can be up to 8.5 or up to about8.0. Preferably, at least one alkaline material is added, either singlyor in combination with at least one second material.

Examples of suitable alkaline materials include aqueous alkali metalsilicates, e.g. any of those defined above, preferably sodium silicate;aqueous alkali metal hydroxides, e.g. sodium and potassium hydroxides,preferably sodium hydroxide; ammonium hydroxide; alkaline aluminumsalts, e.g. aluminates, suitably aqueous aluminates, e.g. sodium andpotassium aluminates, preferably sodium aluminate.

Examples of suitable second materials include aluminum compounds andorganic nitrogen-containing compounds. Examples of suitable aluminumcompounds include neutral and essentially neutral aluminum salts, e.g.aluminum nitrate, alkaline aluminum salts, e.g. any of those definedabove, preferably sodium aluminate.

Examples of suitable organic nitrogen-containing compounds includeprimary amines, secondary amines, tertiary amines and quaternary amines,the latter also referred to as quaternary ammonium compounds. Thenitrogen-containing compound is preferably water-soluble orwater-dispersible. The amine can be uncharged or cationic. Examples ofcationic amines include acid addition salts of primary, secondary andtertiary amines and, preferably, quaternary ammonium compounds, as wellas their hydroxides. The organic nitrogen-containing compound usuallyhas a molecular weight below 1,000, suitably below 500 and preferablybelow 300. Preferably, a low molecular weight organicnitrogen-containing compound is used, for example those compounds havingup to 25 carbon atoms, suitably up to 20 carbon atoms, preferably from 2to 12 carbon atoms and most preferably from 2 to 8 carbon atoms. In apreferred embodiment, the organic nitrogen-containing compound has oneor more oxygen-containing substituents, for example with oxygen in theform of hydroxyl groups and/or alkyloxy groups. Examples of preferredsubstituents of this type include hydroxy alkyl groups, e.g. ethanolgroups, and methoxy and ethoxy groups. The organic nitrogen-containingcompounds may include one or more nitrogen atoms, preferably one or two.Preferred amines include those having a pKa value of at least 6,suitably at least 7 and preferably at least 7.5.

Examples of suitable primary amines, i.e. amines having one organicsubstituent, include alkyl amines, e.g. propyl amine, butyl amine andcyclohexyl amine; alkanol amines, e.g. ethanol amine; and alkoxyalkylamines, e.g. 2-methoxyethyl amine. Examples of suitable secondaryamines, i.e. amines having two organic substituents, include dialkylamines, e.g. diethyl amine, dipropyl amine and di-isopropyl amine;dialkanol amines, e.g. diethanol amine, and pyrrolidine. Examples ofsuitable tertiary amines, i.e. amines having three organic substituents,include trialkyl amines, e.g. triethyl amine; trialkanol amines, e.g.triethanol amine; N,N-dialkyl alkanol amines, e.g. N,N-dimethyl ethanolamine. Examples of suitable quaternary amines, or quaternary ammoniumcompounds, i.e. amines having four organic substituents, includetetraalkanol amines, e.g. tetraethanol ammonium hydroxide andtetraethanol ammonium chloride; quaternary amines or ammonium compoundswith both alkanol and alkyl substituents such as N-alkyltrialkanolamines, e.g. methyltriethanol ammonium hydroxide and methyltriethanolammonium chloride; N,N-dialkyldialkanol amines, e.g. dimethyl diethanolammonium hydroxide and dimethyl diethanol ammonium chloride;N,N,N-trialkyl alkanol amines, e.g. choline hydroxide and cholinechloride; N,N,N-trialkyl benzyl amines, e.g. dimethyl cocobenzylammonium hydroxide, dimethyl cocobenzyl ammonium chloride and trimethylbenzyl ammonium hydroxide; tetraalkyl ammonium salts, e.g. tetramethylammonium hydroxide, tetramethyl ammonium chloride, tetraethyl ammoniumhydroxide, tetraethyl ammonium chloride, tetra-propyl ammoniumhydroxide, tetrapropyl ammonium chloride, diethyldimethyl ammoniumhydroxide, diethyldimethyl ammonium chloride, triethylmethyl ammoniumhydroxide and triethylmethyl ammonium chloride. Examples of suitablediamines include amino-alkylalkanol amines, e.g. aminoethylethanolamine, piperazine and nitrogen-substituted piperazines having one or twolower alkyl groups of 1 to 4 carbon atoms. Examples of preferred organicnitrogen-containing compounds include triethanol amine, diethanol-amine,dipropyl amine, aminoethyl ethanol amine, 2-methoxyethyl amine,N,N-dimethyl-ethanol amine, choline hydroxide, choline chloride,tetramethyl ammonium hydroxide, tetraethyl ammonium hydroxide andtetraethanol ammonium hydroxide.

Preferably, aqueous alkali metal silicate is added, either singly or incombination with aqueous sodium aluminate or aqueous organicnitrogen-containing compound.

When using aqueous alkali metal silicate in step (d) of the process ofthe invention, the aqueous alkali metal silicate is usually added to thereaction vessel at a rate of at least about 300 or at least about 350and suitably at least about 400 or at least about 450 g SiO₂ per hourand kg ion exchange resin present in the reaction vessel. Usually, therate is up to about 10000 or up to about 7000, suitably up to about5,000 and preferably up to about 4000 g SiO₂ per hour and kg ionexchange resin present in the reaction vessel.

When using two or more materials comprising at least one alkalinematerial and at least one second material, the materials can be added inany order, preferably the alkaline material is added first followed byadding the second material.

In one embodiment, alkali metal silicate, e.g. sodium silicate, is addedfirst and then an alkaline aluminum salt, e.g. aqueous sodium aluminate,is added. In another embodiment, aqueous alkali metal hydroxide, e.g.sodium hydroxide, is added first and then an alkaline aluminum salt,e.g. aqueous sodium aluminate, is added. The addition of aluminumcompound provides an aluminated silica-based sol. Suitably, the additionof aluminum compound results in aluminum modification of thesilica-based particles, preferably the particles are surface-modified byaluminum. The amount of aluminum compound used can be varied within widelimits. Usually the amount of aluminum compound added corresponds to amole ratio of Si:Al of from about 1:1 to about 40:1, suitably from about3:1 to about 30:1 and preferably from about 5:1 to about 20:1.

In another embodiment, alkali metal silicate, e.g. sodium silicate, isadded first and then an organic nitrogen-containing compound, e.g.aqueous choline hydroxide, is added. In another embodiment, aqueousalkali metal hydroxide, e.g. sodium hydroxide, is added first and thenan organic nitrogen-containing compound, e.g. aqueous choline hydroxide,is added. The addition of organic nitrogen-containing compound providesa nitrogen-modified silica-based sol. The amount of organicnitrogen-containing compound used can be varied within wide limits.Usually the amount of organic nitrogen-containing compound addedcorresponds to a mole ratio of Si:N of from 1:1 to 50:1, suitably from2:1 to 40:1 and preferably from 2.5:1 to 25:1.

According to one embodiment of the invention, step (d) of the processcomprises keeping or maintaining the temperature of the aqueous phasewhile adding said one or more alkaline materials to the aqueous phase atfrom at least about 0° C., suitably at least about 5° C. and preferablyat least about 10° C. up to about 80° C. or up to 50° C., suitably up toabout 40° C. and preferably up to about 35° C. This can be achieved bycooling or controlling the temperature of the reaction vessel whileadding said one or more alkaline materials to the aqueous phase.

If desired, additional water can be to the reaction vessel during orafter step (d) to lower the viscosity of the aqueous phase and reducethe speed of particle growth, particle aggregation and formation ofelongated aggregates of silica-based particles.

In step (e) of the process, the ion exchange resin is separated from theaqueous phase, for example by filtration. This can be done after step(c), for example after step (c) but before step (d), or after step (d).It is also possible to separate the ion exchange resin from the aqueousphase during step (d). For example, the ion exchange resin can beseparated after adding an alkaline material but before adding a secondmaterial. It is also possible to add part of one alkaline material, e.g.aqueous alkali metal silicate, then separating the ion exchange resinfrom the aqueous phase followed by adding the remaining part of thealkaline material. Preferably, the ion exchange resin is separated fromthe aqueous phase after step (d).

The concentration of the aqueous starting materials used in the process,e.g. the aqueous alkali metal silicate, aqueous alkali metal hydroxideand aqueous sodium aluminate, is preferably adjusted so as to provide asilica-based sol having the silica (SiO₂) contents as defined above.

If desired, the silica-based sol obtained after separating the ionexchange resin from the aqueous phase can be subjected to concentration.This can be carried out in known manner such as, for example, by osmoticmethods, evaporation and ultrafiltration. The concentration can becarried out to provide a silica-based sol having the silica contents asdefined above.

The silica-based sol according to this invention is suitable for use asa flocculating agent, for example in the production of pulp and paper,notably as a drainage and retention aid, and within the field of waterpurification, both for purification of different kinds of waste waterand for purification specifically of white water from the pulp and paperindustry. The silica-based sols can be used as a flocculating agent,notably as a drainage and retention aid, in combination with organicpolymers which can be selected from anionic, amphoteric, non-ionic andcationic polymers and mixtures thereof. The use of such polymers asflocculating agents and as drainage and retention aids is well known inthe art. The polymers can be derived from natural or synthetic sources,and they can be linear, branched or cross-linked. Examples of generallysuitable organic polymers include anionic, amphoteric and cationicstarches; anionic, amphoteric and cationic acrylamide-based polymers,including essentially linear, branched and cross-linked anionic andcationic acrylamide-based polymers; as well as cationicpoly(diallyl-dimethyl ammonium chloride); cationic polyethylene imines;cationic polyamines; cationic poly-amideamines and vinylamide-basedpolymers, melamine-formaldehyde and urea-formalde-hyde resins. Suitably,the silica-based sols are used in combination with at least one cationicor amphoteric polymer, preferably cationic polymer. Cationic starch andcationic polyacrylamide are particularly preferred polymers and they canbe used singly, together with each other or together with otherpolymers, e.g. other cationic and/or anionic polymers. The weightaverage molecular weight of the polymer is suitably above 1,000,000 andpreferably above 2,000,000. The upper limit of the weight averagemolecular weight of the polymer is not critical; it can be about50,000,000, usually 30,000,000 and suitably about 25,000,000. However,the weight average molecular weight of polymers derived from naturalsources may be higher.

The present silica-based sol can also be used in combination withcationic coagulant(s), either with or without the co-use of the organicpolymer(s) described above. Examples of suitable cationic coagulantsinclude water-soluble organic polymeric coagulants and inorganiccoagulants. The cationic coagulants can be used singly or together, i.e.a polymeric coagulant can be used in combination with an inorganiccoagulant. Examples of suitable water-soluble organic polymeric cationiccoagulants include cationic polyamines, polyamideamines, polyethyleneimines, dicyandiamide condensation polymers and polymers of watersoluble ethylenically unsaturated monomer or monomer blend which isformed of 50 to 100 mole % cationic monomer and 0 to 50 mole % othermonomer. The amount of cationic monomer is usually at least 80 mole %,suitably 100 mole %. Examples of suitable ethylenically unsaturatedcationic monomers include dialkylaminoalkyl (meth)-acrylates andacrylamides, preferably in quaternised form, and diallyl dialkylammonium chlorides, e.g. diallyl dimethyl ammonium chloride (DADMAC),preferably homopolymers and copolymers of DADMAC. The organic polymericcationic coagulants usually have a weight average molecular weight inthe range of from 1,000 to 700,000, suitably from 10,000 to 500,000.Examples of suitable inorganic coagulants include aluminum compounds,e.g. alum and polyaluminum compounds, e.g. polyaluminum chlorides,polyaluminum sulphates, polyaluminum silicate sulphates and mixturesthereof.

The components of the drainage and retention aids according to theinvention can be added to the stock, or aqueous cellulosic suspension,in conventional manner and in any order. When using drainage andretention aids comprising a silica-based sol and organic polymer, it ispreferred to add the organic polymer to the stock before adding thesilica-based sol, even if the opposite order of addition may be used. Itis further preferred to add the organic polymer before a shear stage,which can be selected from pumping, mixing, cleaning, etc., and to addthe silica-based sol after that shear stage. When using drainage andretention aids comprising a silica-based sol and anionic and cationicorganic polymers, it is preferred to add the cationic organic polymer tothe stock before adding the silica-based sol and anionic organicpolymer. When using a cationic coagulant, it is preferably added to thecellulosic suspension before the addition of the silica-based sol,preferably also before the addition of the organic polymer(s).

The components of the drainage and retention aids according to theinvention are added to the stock to be dewatered in amounts which canvary within wide limits depending on, inter alia, type and number ofcomponents, type of furnish, filler content, type of filler, point ofaddition, etc. Generally the components are added in amounts that givebetter drainage and retention than is obtained when not adding thecomponents. The silica-based sol is usually added in an amount of atleast about 0.001% by weight, often at least about 0.005% by weight,calculated as SiO₂ and based on dry furnish, i.e. dry cellulosic fibersand optional fillers, and the upper limit is usually about 1.0% byweight and suitably about 0.5% by weight. Each of the organic polymersis usually added in an amount of at least about 0.001% by weight, oftenat least about 0.005% by weight, based on dry furnish, and the upperlimit is usually about 3% by weight and suitably about 1.5% by weight.When using a cationic polymeric coagulant, it can be added in an amountof at least about 0.05% by weight, based on dry furnish. Suitably, theamount is in the range of from about 0.07 to about 0.5% by weight,preferably in the range from about 0.1 to about 0.35% by weight. Whenusing an aluminum compound as the inorganic coagulant, the total amountadded is usually at least about 0.05% by weight, calculated as Al₂O₃ andbased on dry furnish. Suitably the amount is in the range of from about0.1 to about 3.0% by weight, preferably in the range from about 0.5 toabout 2.0% by weight.

Further additives which are conventional in papermaking can of course beused in combination with the additives according to the invention, suchas, for example, dry strength agents, wet strength agents, opticalbrightening agents, dyes, sizing agents like rosin-based sizing agentsand cellulose-reactive sizing agents, e.g. alkyl and alkenyl ketenedimers and ketene multimers, alkyl and alkenyl succinic anhydrides, etc.The cellulosic suspension, or stock, can also contain mineral fillers ofconventional types such as, for example, kaolin, china clay, titaniumdioxide, gypsum, talc and natural and synthetic calcium carbonates suchas chalk, ground marble and precipitated calcium carbonate.

The process of this invention is used for the production of paper. Theterm “paper”, as used herein, of course include not only paper and theproduction thereof, but also other cellulosic sheet or web-likeproducts, such as for example board and paperboard, and the productionthereof. The process can be used in the production of paper fromdifferent types of suspensions of cellulose-containing fibers and thesuspensions should suitably contain at least about 25% by weight andpreferably at least about 50% by weight of such fibers, based on drysubstance. The suspension can be based on fibers from chemical pulp suchas sulphate, sulphite and organosolv pulps, mechanical pulp such asthermomechanical pulp, chemo-thermomechanical pulp, refiner pulp andgroundwood pulp, from both hardwood and softwood, and can also be basedon recycled fibers, optionally from de-inked pulps, and mixturesthereof. The pH of the suspension, the stock, can be within the range offrom about 3 to about 10. The pH is suitably above about 3.5 andpreferably within the range of from about 4 to about 9.

The invention is further illustrated in the following example which,however, is not intended to limit the same. Parts and % relate to partsby weight and % by weight, respectively, unless otherwise stated.

Example 1

The following equipment and starting materials were used to producesilica-based sols according to the invention, unless otherwise stated:

-   -   (a) Reactor equipped with a stirrer;    -   (b) Ion exchange resin Amberlite™ IRC84SPI (available from Rohm        & Haas) which was regenerated with sulphuric acid according to        manufacturer's instruction;    -   (c) Aqueous sodium silicate solution having a SiO₂ content of        about 23.9 wt. % and mole ratio of SiO₂ to Na₂0 of about 3.4;        and    -   (d) Aqueous sodium aluminate solution containing about 24.5 wt.        % Al₂O₃.

Example 2

This example illustrates the preparation of a silica-based sol accordingto the invention:

Regenerated ion exchange resin (400 g) and water (1350 g) were added toa reactor. The obtained slurry was stirred and kept at a temperature ofabout 21° C. throughout the reaction. Aqueous sodium silicate (449 g)was added to the slurry during 5.5 min (addition rate of 2927 gSiO₂/(h×kg ion exchange resin)). The slurry was then stirred for about19 minutes, whereupon the pH of the aqueous phase was about 7.4. Water(6×200 g) was added to the slurry during a period of 17 minutes,whereupon the slurry was further stirred for another 36 minutes untilthe pH was about 7.2. Aqueous sodium aluminate (33 g) was diluted withwater (297 g) and the obtained dilute sodium aluminate solution wasadded to the slurry during 5 min whereupon the stirring was continuedfor 9 min and the obtained silica-based sol was then separated from theion exchange resin.

The obtained sol of silica-based particles, designated Ex. 2, had a SiO₂content of 3.1 wt. %, mole ratio Si:Na of 9.4, mole ratio Si:Al of 9.8,pH of 7.7, viscosity of 96 cP, axial ratio of 30, specific surface areaof 1210 m²/g and S-value of 6%.

Example 3

This example illustrates the preparation of another silica-based solaccording to the invention:

Regenerated ion exchange resin (332 g) and water (1350 g) were added toa reactor. The obtained slurry was stirred and kept at a temperature ofabout 21° C. throughout the reaction. Aqueous sodium silicate (449 g)was added to the slurry during 5.5 min (addition rate of 3526 gSiO₂/(h×kg ion exchange resin)). The slurry was then stirred for about55 minutes, whereupon the pH of the aqueous phase was about 7.6. Water(4×200 g) was added to the slurry during a period of 15 minutes,whereupon the slurry was further stirred for another 44 minutes untilthe pH was about 7.5. Aqueous sodium aluminate (33 g) was diluted withwater (297 g) and the obtained dilute sodium aluminate solution wasadded to the slurry during 4 min whereupon the stirring was continuedfor 5 min and the obtained silica-based sol was then separated from theion exchange resin.

The obtained sol of silica-based particles, designated Ex. 3, had a SiO₂content of 3.6 wt. %, mole ratio Si:Na of 10.3; mole ratio of Si:Al of10.6, pH of 8.2, viscosity of 30 cP, axial ratio of 18, specific surfacearea of 1080 m²/g and S-value of 8%.

Example 4

This example illustrates the preparation of yet another silica-based solaccording to the invention:

Regenerated ion exchange resin (400 g) and water (1350 g) were added toa reactor. The obtained slurry was stirred and kept at a temperature ofabout 21° C. throughout the reaction. Aqueous sodium silicate (449 g)was added to the slurry during 5.5 min (addition rate of 2927 gSiO₂/(h×kg ion exchange resin)). The slurry was then stirred for about20 minutes, whereupon the pH of the aqueous phase was about 7.4. Aqueoussodium aluminate (33 g) was diluted with water (297 g) and the obtaineddilute sodium aluminate solution was added to the slurry during 3 mintogether with additional water (440 g) whereupon the stirring wascontinued for 15 min. More water (440 g) was added to the slurry and theobtained silica-based sol was then separated from the ion exchangeresin.

The obtained sol of silica-based particles, designated Ex. 4, had a SiO₂content of 3.6 wt. %, mole ratio Si:Na of 10.9, mole ratio of Si:Al of10.9, pH of 8.3, viscosity of 22 cP, axial ratio of 14, specific surfacearea of 1200 m²/g and S-value of 8%.

Example 5

This example illustrates the preparation of still another silica-basedsol according to the invention:

Regenerated ion exchange resin (4500 l; 5130 kg) and water (22 cubicmeters) were added to a reactor. The obtained slurry was stirred andkept at a temperature of about 29° C. throughout the reaction. Aqueoussodium silicate (4400 kg; 29% by weight SiO₂) was added to the slurry ata rate of 8000 kg/h, corresponding to 452 g SiO₂/(h×kg ion exchangeresin). The slurry was then stirred for about 5 to 10 min, whereupon thepH of the aqueous phase was about 7. Additional aqueous sodium silicate(1600 kg) was added to the slurry at a rate of 8000 kg/h, and thenaqueous sodium aluminate (650 kg) was added at a rate of 650 kg/htogether with additional water (5300 kg/h) in line, whereupon thestirring was continued for 15 min. The aqueous phase was separated fromthe ion exchange resin while adding additional water (3000 kg), and theobtained sol of silica-based particles was subjected to ultrafiltration.

The obtained sol of silica-based particles, designated Ex. 5, had a SiO₂content of 6.5 wt. %, mole ratio Si:Na of 10, mole ratio of Si:Al of 10,pH of 8.3, viscosity of 22 cP, axial ratio of 14, specific surface areaof 1100 m²/g and S-value of 14%.

Example 6

This example illustrates the preparation of another silica-based solaccording to the invention:

Regenerated ion exchange resin (3815 kg) and water (21099 kg) were addedto a reactor. The obtained slurry was stirred and kept at a temperatureof about 25° C. throughout the reaction. Aqueous sodium silicate (4416kg) was added to the slurry (addition rate of 623 g SiO₂/(h×kg ionexchange resin)). The slurry was then stirred for 9 minutes, whereuponthe pH of the aqueous phase was about 7.5. Additional aqueous sodiumsilicate (1577 kg) was added to the slurry at a rate of 7278 kg/h, andthen aqueous sodium aluminate (644 kg) was added at a rate of 1380 kg/htogether with additional water (6007 kg). The obtained silica-based solwas separated from the ion exchange resin while adding additional water(4000 kg) to the slurry, and then subjected to ultra filtration.

The obtained sol of silica-based particles, designated Ex. 6, had a SiO₂content of 6.6 wt. %, mole ratio Si:Na of 9, mole ratio of Si:Al of 9,pH of 8.3, viscosity of 146 cP, axial ratio of 19, specific surface areaof 1110 m²/g and S-value of 12%.

Example 7

This example illustrates the preparation of yet another silica-based solaccording to the invention:

Regenerated ion exchange resin (3745 kg) and water (20845 kg) were addedto a reactor. The obtained slurry was stirred and kept at a temperatureof about 28° C. throughout the reaction. Aqueous sodium silicate (4599kg) was added to the slurry during 30 min (addition rate of 705 gSiO₂/(h×kg ion exchange resin)). The slurry was then stirred for another12 minutes, whereupon the pH of the aqueous phase was about 7.4.Additional aqueous sodium silicate (1348 kg) was added to the slurry ata rate of 6221 kg/h, and then aqueous sodium aluminate (601 kg) wasadded at a rate of 522 kg/h together with additional water (6007 kg).The obtained silica-based sol was separated from the ion exchange resinwhile adding additional water (4000 kg) to the slurry, and thensubjected to ultra filtration.

The obtained sol of silica-based particles, designated Ex. 7, had a SiO₂content of 6.5 wt. %, mole ratio Si:Na of 8, mole ratio of Si:Al of 9,pH of 7.8, viscosity of 115 cP, axial ratio of 18, specific surface areaof 1000 m²/g and S-value of 12%.

Example 8

This example illustrates the preparation of another silica-based solaccording to the invention:

Regenerated ion exchange resin (4500 l; 5130 kg) and water (21 cubicmeters) were added to a reactor. The obtained slurry was stirred andkept at a temperature of about 29° C. throughout the reaction. Aqueoussodium silicate (4400 kg; 29% by weight SiO₂) was added to the slurry ata rate of 7500 kg/h, corresponding to 420 g SiO₂/(h×kg ion exchangeresin). The slurry was then stirred for about 9 min, whereupon the pH ofthe aqueous phase was about 7. Additional aqueous sodium silicate (1800kg) was added to the slurry at a rate of 7500 kg/h, and then aqueoussodium aluminate (600 kg) was added at a rate of 650 kg/h together withadditional water (5300 kg/h) in line, whereupon the stirring wascontinued for 15 min. The aqueous phase was separated from the ionexchange resin while adding additional water (3000 kg), and the obtainedsol of silica-based particles was subjected to ultra filtration.

The obtained sol of silica-based particles, designated Ex. 8, had a SiO₂content of 7.4 wt. %, mole ratio Si:Na of 10, mole ratio of Si:Al of 10,pH of 8.8, viscosity of 11 cP, axial ratio of 11.9, specific surfacearea of 1060 m²/g and S-value of 17%.

Example 9

The following products were used for comparison purposes in the drainageand retention performance tests of the Examples:

Ref. 1 is a silica sol commercially available under the trade name Nalco8691 which had a pH of 10.9, viscosity of 3 cP, SiO₂ content of 11.4,axial ratio of 7 and S-value of 35%, and contained silica particles witha specific surface area of 800 m²/g.

Ref. 2 is a silica-based sol prepared according to the generaldisclosure of WO 00/66491 which had a pH of 10,6, viscosity of 8 cP,SiO₂ content of 15, mole ratio Si:Na of 11, axial ratio of 8 and S-valueof 35%, and contained silica-based particles with a specific surfacearea of 720 m²/g.

Ref. 3 is a silica-based sol prepared according to the generaldisclosure of U.S. Pat. No. 5,368,833 which had a pH of 9, viscosity of5 cP, SiO₂ content of 7.8, mole ratio Si:Na of 17, mole ratio Si:Al of19, axial ratio of 9 and S-value of 21%, and contained silica-basedparticles with a specific surface area of 810 m²/g.

Ref. 4 is bentonite in the form of an aqueous suspension

Example 10

The following procedures and equipment were used to evaluate theperformance of silica-based sols according to the invention and productsused for comparison:

Drainage performance was evaluated by means of a Dynamic DrainageAnalyser (DDA), available from Akribi AB, Sweden, which measures thetime for draining a set volume of stock. The stock was stirred in abaffled jar at a speed of 1500 rpm throughout the test while additionsof chemicals were made. A stock volume of 800 ml was drained through awire when removing a plug and applying vacuum to that side of the wireopposite to the side on which the stock is present. Drainage performanceis reported as the dewatering time (s). The additions were madeaccording to the following general sequence:

-   -   (i) adding component D, if any, to the stock followed by        stirring for (d) seconds,    -   (ii) adding component C, if any, to the stock followed by        stirring for (c) seconds,    -   (iii) adding component B to the stock followed by stirring        for (b) seconds,    -   (iv) adding component A to the stock followed by stirring        for (a) seconds, and    -   (v) dewatering the stock while automatically recording the        dewatering time.

The addition levels of polymers and bentonite were calculated as dryproduct on dry stock system, the addition levels of poly aluminumchloride were calculated as Al₂O₃ and based on dry stock system, and theaddition level of silica or silica-based sols were calculated as SiO₂and based on dry stock system.

Retention performance (first pass retention) was evaluated by means of anephelometer by measuring the turbidity of the filtrate from the DynamicDrainage Analyser (DDA), the white water, obtained by draining the stockobtained in the drainage performance test. Turbidity is reported innephelometric units (NTU).

Example 11

Drainage and retention performance was evaluated according to thegeneral procedure of Example 10.

The cellulosic suspension, or stock, used in this Example was based on afurnish from a board mill producing liquid packaging board based on 50%by weight of peroxide bleached sulphate pulp and 50% by weight ofuncoated broke. Stock consistency was 4.7 g/l, pH about 7.7,conductivity 1800 μS/cm, Ca²⁺ ion content 40 mg/l and cationicdemand−195 μeq./l. Component B was cationic starch (Perlbond 930) addedin an amount of 10 kg/t followed by stirring for 15 seconds. Component Awas either Ref. 1 or Ex. 5 added in varying amounts followed by stirringfor 5 seconds. Table 1 shows the results at varying dosages of SiO₂.

TABLE 1 SiO₂ Turbidity Test Dosage Dewatering Time [s] [NTU] No. [kg/t]Ref. 1 Ex. 5 Ref. 1 Ex. 5 1 0 28.6 28.6 92 92 2 0.5 26 22.3 83 82 3 120.3 16 79 79 4 1.5 18.7 17 72 71

Example 12

Drainage and retention performance was evaluated according to thegeneral procedure of Example 10 using the stock of Example 11.

Component C was poly aluminum chloride (Eka ATC 8210) added in an amountof 0.3 kg/t followed by stirring for 10 seconds. Component B wascationic starch (Perlbond 930) added in an amount of 10 kg/t followed bystirring for 15 seconds. Component A was either Ref. 1 or Ex. 5 added invarying amounts followed by stirring for 5 seconds. Table 2 shows theresults at various dosages of SiO₂.

TABLE 2 SiO₂ Turbidity Test Dosage Dewatering time [s] [NTU] No. [kg/t]Ref. 1 Ex. 5 Ref. 1 Ex. 5 1 0 26.7 26.7 87 87 2 0.25 21.7 19.9 86 76 30.5 18.7 17.1 84 74 4 1 15.7 14.3 76 75 5 1.5 13.7 12.9 77 76

Example 13

Drainage and retention performance was evaluated according to thegeneral procedure of Example 10 using the stock of Example 11.

Component D was a highly charged, low molecular weight cationicpolyacrylamide (Eka ATC 5439) added in an amount of 0.3 kg/t followed bystirring for 10 seconds. Component C was a high molecular weight,cationic polyacrylamide (Eka PL 1510) added in an amount of 0.2 kg/tfollowed by stirring for 5 seconds. Component B was cationic starch(Perlbond 930) added in an amount of 5 kg/t followed by stirring for 20seconds. Component A was either Ref. 1 or Ex. 5 added in varying amountsfollowed by stirring for 5 seconds. Table 3 shows the results at variousdosages of SiO₂.

TABLE 3 SiO₂ Turbidity Test Dosage Dewatering time [s] [NTU] No. [kg/t]Ref. 1 Ex. 5 Ref. 1 Ex. 5 1 0 26.7 26.7 87 87 2 0.25 21.7 19.9 86 76 30.5 18.7 17.1 84 74 4 1 15.7 14.3 76 75 5 1.5 13.7 12.9 77 76

Example 14

Drainage and retention performance was evaluated according to thegeneral procedure of Example 10 using the stock of Example 11.

Component C was cationic starch (Perlbond 970) added in an amount of 8kg/t followed by stirring for 15 seconds. Component B was a highmolecular weight, anionic polyacrylamide (Eka PL 8660) added in anamount of 0.25 kg/t followed by stirring for 10 seconds. Component A waseither Ref. 2 or Ex. 5 added in varying amounts followed by stirring for5 seconds. Table 4 shows the results at various dosages of SiO₂.

TABLE 4 SiO₂ Turbidity Test Dosage Dewatering time [s] [NTU] No. [kg/t]Ref. 2 Ex. 5 Ref. 2 Ex. 5 1 0 28.5 28.5 109 109 2 0.1 21.8 23.3 128 93 30.25 18.3 17.4 112 95 4 0.5 12.6 12.5 105 95 5 1 8.5 8 85 80 6 1.5 6.96.7 85 73

Example 15

Drainage and retention performance was evaluated according to thegeneral procedure of Example 10 using the stock of Example 11.

Component C was cationic starch (Perlbond 970) added in an amount of 8kg/t followed by stirring for 15 seconds. Component B was a highmolecular weight, cationic polyacrylamide (Eka PL 1510) added in anamount of 0.25 kg/t followed by stirring for 10 seconds. Component A waseither Ref. 2 or Ex. 5 added in varying amounts followed by stirring for5 seconds. Table 5 shows the results at various dosages of SiO₂.

TABLE 5 SiO₂ Turbidity Test Dosage Dewatering time [s] [NTU] No. [kg/t]Ref. 2 Ex. 5 Ref. 2 Ex. 5 1 0 29.3 29.3 170 170 2 0.25 20.2 14.8 143 1253 0.5 13 10.3 126 106 4 1 7.9 7.1 103 95

Example 16

Drainage and retention performance was evaluated according to thegeneral procedure of Example 10.

The stock used in this Example was based on furnish from a fine papermill producing uncoated copy paper containing about 65% by weighteucalyptus fibers and about 35% by weight PCC. Consistency was 12.5 g/land pH was about 7.1.

Component B was cationic starch (Amylofax 2200) added in an amount of 5kg/t followed by stirring for 20 seconds. Component A was either Ref. 3or Ex. 5 added in varying amounts followed by stirring for 10 seconds.Table 6 shows the results at various dosages of SiO₂.

TABLE 6 SiO₂ Turbidity Test Dosage Dewatering time [s] [NTU] No. [kg/t]Ref. 3 Ex. 5 Ref. 3 Ex.5 1 0 20.1 20.1 340 340 2 0.2 19.1 17.6 285 263 30.3 17 15.2 258 223 4 0.4 14.5 13.6 235 186 5 0.6 15.5 11.7 202 156

Example 17

Drainage and retention performance was evaluated according to thegeneral procedure of Example 10 using a stock similar to the one ofExample 16 but furnish was taken from the secondary cleaner reject ofthe paper machine and the consistency was about 15 g/l.

Component C was cationic starch (Amylofax 2200) added in an amount of 10kg/t followed by stirring for 20 seconds. Component B was a highmolecular weight, cationic polyacrylamide (Eka PL 1710) added in anamount of 0.2 kg/t followed by stirring for 10 seconds. Component A waseither Ref. 2 or Ex. 5 added in varying amounts followed by stirring for10 seconds. Table 7 shows the results at various dosages of SiO₂.

TABLE 7 SiO₂ Turbidity Test Dosage Dewatering time [s] [NTU] No. [kg/t]Ref. 2 Ex.5 Ref. 2 Ex. 5 1 0 7.1 7.1 205 205 2 0.1 6.7 6.3 134 117 3 0.26.9 5.6 117 102 4 0.3 5.6 4.8 102 95 5 0.4 5.9 4.6 94 82

Example 18

Drainage and retention performance was evaluated according to thegeneral procedure of Example 10.

The stock used in this Example was based on furnish from a board millproducing liquid packaging board containing bleached sulphate pulp of60% by weight birch and 40% by weight spruce/pine. Stock consistency was6.3 g/l, pH about 8.3 and conductivity 1000 μS/cm.

Component B was cationic starch (HiCat 142) added in an amount of 6 kg/tfollowed by stirring for 15 seconds. Component A was either Ref. 4 orEx. 5 added in varying amounts followed by stirring for 5 seconds. Table8 shows the results at various dosages of component A.

TABLE 8 Test A Dewatering time [s] No. Dosage [g/t] Ref. 4 Ex. 5 1 018.9 18.9  2 300 17.6 10.8  3 600 15.1 7.2 4 1200 10.9 6.3 5 2000 9.35.5 6 4000 7.5 NA 7 8000 8.4 NA

Example 19

Drainage and retention performance was evaluated according to thegeneral procedure of Example 10.

The stock used in this Example was from a liner mill producing white topliner consisting of a white top ply and a brown bottom ply. The whitetop ply stock was used and had a consistency of 8.4 g/l, pH of about 8.7and conductivity of 800 μS/cm. Before the additions of components C, Band A, 100 kg/t of the PCC filler (Hypercarb FS260) was added separatelyto each test sample.

Component C was cationic starch (PB tapioka) added in an amount of 10kg/t followed by stirring for 15 seconds. Component B was a cationicpolyacrylamide (Percol 292NS) added in an amount of 0.4 kg/t followed bystirring for 20 seconds. Component A was Ref. 4, Ref. 3 or Ex. 5 addedin varying amounts followed by stirring for 10 seconds. Table 9 showsthe results at various dosages of component A.

TABLE 9 Test A Dewatering time [s] No. Dosage [kg/t] Ref. 4 Ref. 3 Ex. 51 0 15.3 15.3 15.3  2 0.1 NA 13.4 11.6  3 0.2 NA 10.9 9.4 4 0.4 NA  8.87.9 5 0.6 NA  7.8 7.6 6 1 13.7 NA NA 7 2 11.9 NA NA 8 3 11.4 NA NA 9 410.4 NA NA

Example 20

Drainage and retention performance was evaluated according to thegeneral procedure of Example 10. The stock used in this Example was froma liner mill producing two-ply liner consisting of recycled pulp. Thestock had a consistency of 13.5 g/l, pH of about 6.4 and conductivity of2000 μS/cm.

Component B was a high molecular weight, cationic polyacrylamide (Eka PL1510) added in an amount of 0.75 kg/t followed by stirring for 10seconds. Component A was either Ref. 3 or Ex. 5 added in varying amountsfollowed by stirring for 10 seconds. Table 10 shows the results atvarious dosages of SiO₂.

TABLE 10 SiO₂ Turbidity Test Dosage Dewatering time [s] [NTU] No. [kg/t]Ref. 3 Ex. 5 Ref. 3 Ex. 5 1 0 12.3 12.3 250 250 2 0.1 10 9.4 240 223 30.2 9.3 8.1 220 220 4 0.3 9.2 7.9 238 214

Example 21

Retention performance was evaluated by means of a Dynamic Drainage Jar(DDJ), available from Paper Research Materials, Inc., which measures thefines retention when draining a set volume of stock. The stock wasstirred in a baffled jar at a speed of 1200 rpm throughout the test. Astock volume of 500 ml was used and additions of chemicals were made.The stock was drained through a wire when opening a tube clamp, the tubeconnected to an opening in the bottom of the jar below the wire.Drainage was collected in a beaker during 30 seconds at a flow ratepartly set by the size of a tip opening connected to the tube. Flow ratewas approximately 130-160 ml/min. The amount of dry material in thebeaker was determined by evaporation at 105° C. in an oven. The totalfines fraction was determined separately. The results were reported asfines retention (%).

The additions of chemicals were made according to the general sequenceof Example 10.

The stock used in this Example was based on a furnish containingchemical pulp of 80% hardwood and 20% softwood. The furnish contained50% of this pulp and 50% ground calcium carbonate. Salts were added tocreate a conductivity of about 1.5 mS/cm, pH was about 8.1 to 8.2 andthe pulp consistency was about 5 g/l.

Component C was a cationic starch (Perlbond 930) added in an amount of10 kg/t followed by stirring for 20 seconds. Component B was a highmolecular weight, cationic polyacrylamide (Eka PL 1510) added in anamount of 0.5 kg/t followed by stirring for 20 seconds. Component A waseither of Ref. 3, Ex. 2, Ex. 4, Ex. 5 or Ex. 7 added in varying amountsfollowed by stirring for 10 seconds. Table 11 shows the results atvarious dosages of SiO₂.

TABLE 11 SiO₂ Test Dosage Fines Retention [%] No. [kg/t] Ref. 3 Ex. 2Ex. 4 Ex. 5 Ex. 7 1 0 27 27 27 27 27 2 0.2 31 45 45 41 42 3 0.35 42 5855 50 54 4 0.5 48 62 60 56 58

Example 22

Drainage performance was evaluated according to the general procedure ofExample 10 using a stock similar to the one used in Example 21.

Component B was a high molecular weight, cationic polyacrylamide (Eka PL1510) added in an amount of 2.0 kg/t followed by stirring for 20seconds. Component A was either of Ref. 3, Ex. 2, Ex. 3, Ex. 4, Ex. 5 orEx. 7 added in varying amounts followed by stirring for 10 seconds.Table 12 shows the results at various dosages of SiO₂.

TABLE 12 SiO₂ Test Dosage Dewatering [s] No. [kg/t] Ref. 3 Ex. 2 Ex. 3Ex. 4 Ex. 5 Ex. 7 1 0 20.0 20.0 20.0  20.0  20.0 20.0 2 0.05 18.2 15.4NA NA 16.3 16.0 3 0.1 15.6 11.4 11.7  12.1  12.6 12.9 4 0.2 11.4 7.8 7.87.5 8.7 8.9 5 0.3 8.4 6.1 6.0 6.0 6.8 6.8 6 0.5 6.2 4.7 4.9 4.4 4.8 4.8

Example 23

Drainage performance was evaluated according to the general procedure ofExample 10 using a stock similar to the one used in Example 21.

Component C was a cationic starch (Perlbond 930) added in an amount of10 kg/t followed by stirring for 15 seconds. Component B was a highmolecular weight, cationic polyacrylamide (Eka PL 1510) added in anamount of 0.5 kg/t followed by stirring for 10 seconds. Component A waseither of Ref. 3, Ex. 2, Ex. 3, Ex. 4, Ex. 5, Ex. 6 or Ex. 7 added invarying amounts followed by stirring for 10 seconds. Table 13 shows theresults at various dosages of SiO₂.

TABLE 13 SiO₂ Test Dosage Dewatering [s] No. [kg/t] Ref. 3 Ex. 2 Ex. 3Ex. 4 Ex. 5 Ex. 6 Ex. 7 1 0 27.2 27.2 27.2 27.2 27.2 27.2 27.2 2 0.121.9 17.7 17.4 18.1 18.5 18.7 19.0 3 0.2 17.3 12.1 12.4 13.5 13.6 13.713.4 4 0.3 14.8 10.4 10.4 10.6 11.9 11.7 11.4 5 0.5 11.8 8.5 8.7 8.8 9.39.5 8.9

Example 24

Axial ratios were measured and calculated as described by D. Biddle, C.Walldal and S. Wall in Colloids and Surfaces, A: Physiochemical andEngineering Aspects 118 (1996), 89-95, determining dimensions and axialratios of equivalent unsolvated prolate ellipsoids. This ellipsoid modelis characterised by the ratio between the longer diameter (a) and theshorter diameter (b), the axial ratio being defined as a/b. The modelused is a combination of data obtained from intrinsic viscositymeasurements and dynamic light scattering measurements and the relationsof Simha and Perrin for the intrinsic viscosity and fractional factorsrespectively of ellipsoids of revolution. These data were then used toiterate a mathematical fit to the ellipsoid form, thus giving an axialratio, a/b.

Table 14 shows axial ratios of Ex. 2, Ex. 3, Ex. 4, Ex. 5, Ex. 6, Ex. 7and Ref. 3 as well as the improvements in retention (R) and dewatering(D) improvements observed in Examples 21, 22 and 23 when using the solsof silica-based particles according to the invention over Ref. 3 at thedosage of 0.5 kg/t SiO₂.

TABLE 14 Retention Dewatering Dewatering Silica- Axial ImprovementImprovement Improvement Based Ratio [%] [%] [%] Sol [a/b] Example 21Example 22 Example 23 Ref. 3 9 0 (ref) 0 (ref) 0 (ref) Ex. 2 30 29 24 28Ex. 3 18 NA 20 26 Ex. 4 14 25 28 25 Ex. 5 14 17 21 21 Ex. 6 19 NA NA 19Ex. 7 18 21 21 25

Example 25

Drainage performance was evaluated according to the general procedure ofExample 10 using a stock similar to the one used in Example 21.

Component B was a high molecular weight, cationic polyacrylamide (Eka PL1510) added in an amount of 0.8 kg/t followed by stirring for 20seconds. Component A was either Ref. 3 or Ex. 8 added in varying amountsfollowed by stirring for 10 seconds. Table 15 shows the results atvarious dosages of SiO₂.

TABLE 15 Test SiO₂ Dewatering time [s] No. Dosage [kg/t] Ref. 3 Ex. 8 10 14.4 14.4 2 0.1 10.5 9.56 3 0.2 8.14 6.65 4 0.4 5.96 5.38

1. Sol containing silica-based particles having an axial ratio of atleast about 10 and specific surface area of at least about 600 m²/g. 2.Sol containing silica-based particles having an axial ratio of at leastabout 10 and S-value up to about
 25. 3. The sol according to claim 1,wherein the axial ratio is in the range of from 10 to
 100. 4. The solaccording to claim 2, wherein the axial ratio is in the range of from 11to
 35. 5. The sol according to claim 1, wherein the silica-basedparticles have a specific surface area in the range of from 800 to 1600m²/g.
 6. The sol according to claim 1, wherein the silica-basedparticles have a specific surface area of at least about 1000 m²/g. 7.The sol according to claim 1, wherein the silica-based particles aresurface-modified with aluminum.
 8. The sol according to claim 1, whereinthe sol has a silica content of at least about 3% by weight.
 9. The solaccording to claim 1, wherein the sol has an S-value in the range offrom about 5 to about 20%.
 10. The sol according to claim 1, wherein thesol has a pH in the range of from about 7.0 to about 10.0.
 11. The solaccording to claim 1, wherein the sol is aqueous. 12.-20. (canceled) 21.The sol according to claim 2, wherein the axial ratio is in the range offrom 10 to
 100. 22. The sol according to claim 21, wherein the axialratio is in the range of from 11 to
 35. 23. The sol according to claim2, wherein the silica-based particles have a specific surface area inthe range of from 800 to 1600 m²/g.
 24. The sol according to claim 2,wherein the silica-based particles have a specific surface area of atleast about 1000 m²/g.
 25. The sol according to claim 2, wherein thesilica-based particles are surface-modified with aluminum.
 26. The solaccording to claim 2, wherein the sol has a silica content of at leastabout 3% by weight.
 27. The sol according to claim 2, wherein the solhas an S-value in the range of from about 5 to about 20%.
 28. The solaccording to claim 2, wherein the sol has a pH in the range of fromabout 7.0 to about 10.0.
 29. The sol according to claim 2, wherein thesol is aqueous.